800G rollout imminent following live trials

During the run-up to what was expected to be a busy OFC 2020 Conference and Exhibition over the past few months, optical equipment manufacturers have been preparing 800G single wavelength coherent solutions for production. Several companies have shared information on recent 800G trials in live carrier networks and have released details of their 800G solutions that are production-ready and will be deployed in carrier networks over the coming months. The introduction of 800G coherent is a significant development supporting throughput per wavelength on metro links that is one third faster than the 600G coherent solutions introduced just two years ago and four to eight times faster than the 100/200G coherent links widely used today.

Maximizing performance with technology evolution
Coherent systems are commonly used for long distance, metro and data center interconnect (DCI) links. The first widespread deployments were 100G links with QPSK modulation and 32Gbaud symbol rates. With subsequent generations, the technology has been developed to support higher baud rates and higher order modulation. Leading vendors working on their own solutions and through industry organizations such as the Optical Internetworking Forum have developed a raft of technologies to support longer reach applications, including submarine, and high bandwidth, metro and DCI applications. A single system can now be used to support 200Gbps to 800Gbps per wavelength and can be configured to maximize performance over a specific distance and fiber link.

The 600G solution was first introduced in 2018 for short reach peer-to-peer applications. Today it has been enhanced by the technology developed for 800G to cover metro distances. For the latest 800G solutions, the symbol rate has been stretched to over 90Gbaud, a very significant step up. To achieve this feat, companies have developed a new generation of 7nm digital signal processors (DSPs) that build on previous designs developed for 400G and 600G. The first of these 800G-capable DSPs were announced at OFC 2019. Since then, companies have completed the silicon devices, developed new modules and line cards, and updated software to support 800G and enhanced capabilities.

The development and trials of 800G per wavelength coherent systems comes in addition to other developments to stretch single fiber capacity. These include the ITU flexible grid, which enables 75GHz spacing and multi-carrier super-channels that significantly increase spectral efficiency, as well as extended C-band spectrum. A standard C-band implementation with 4THz of spectrum and 16QAM modulation for 400Gbps channels and 75GHz channel spacing will deliver a maximum bandwidth of 38.4Tbps, up from 8Tbps for a typical 100Gbps implementation with 50GHz spacing. The extended spectrum of new line systems up to 4.8THz, or 6THz for Huawei's Super C-band, is further improving fiber capacity and maximizing the bandwidth of each single fiber up to 48Tbps.

Maximizing fiber capacity and reducing costs
All these developments are ready for deployment in live carrier networks to maximize fiber capacity and further reduce cost per bit. 800G single wavelength coherent is a significant step up in bandwidth from previous generations. This bandwidth will be particularly useful for metro and DCI links connecting data centers and other locations that will soon be upgraded to 400Gbps switch connections. As the bandwidths demanded by users working from home and businesses delivering services remotely grow rapidly, this upgrade to 800G is likely to be popular.

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